Name Lookup in Nested Class Scope

Normal rules apply for name lookup (§ 7.4.1, p. 283) inside a nested class. Of course, because a nested class is a nested scope, the nested class has additional enclosing class scopes to search. This nesting of scopes explains why we didn’t define line_no inside the nested version of QueryResult. Our original QueryResult class defined this member so that its own members could avoid having to write TextQuery::line_no. Having nested the definition of our results class inside TextQuery, we no longer need this typedef. The nested QueryResult class can access line_no without specifying that line_no is defined in TextQuery.

As we’ve seen, a nested class is a type member of its enclosing class. Members of the enclosing class can use the name of a nested class the same way it can use any other type member. Because QueryResult is nested inside TextQuery, the query member of TextQuery can refer to the name QueryResult directly:

// return type must indicate that QueryResult is now a nested class
TextQuery::QueryResult
TextQuery::query(const string &sought) const
{
    // we'll return a pointer to this set if we don't find sought
    static shared_ptr<set<line_no>> nodata(new set<line_no>);
    // use find and not a subscript to avoid adding words to wm!
    auto loc = wm.find(sought);
    if (loc == wm.end())
        return QueryResult(sought, nodata, file);  // not found
    else
        return QueryResult(sought, loc->second, file);
}

As usual, the return type is not yet in the scope of the class (§ 7.4, p. 282), so we start by noting that our function returns a TextQuery::QueryResult value. However, inside the body of the function, we can refer to QueryResult directly, as we do in the return statements.